A process for producing a thermoplastic polyurethane fiber with low shrinkage, and the use of the fiber

ABSTRACT

A process produces a thermoplastic polyurethane (TPU) fiber with low shrinkage, in particular at a high spinning speed. The resulting fiber can be used for fabric, especially for garments and shoes. The process combines the high-speed spinning process with the heat-setting process. This allows the process to produce a TPU fiber in high productivity, which could greatly decrease the cost. Moreover, the obtained TPU fiber has very low shrinkage of &lt;10%, which makes it well suitable as the main raw material in fabrics.

TECHNICAL FIELD

The present invention relates to a process for producing a thermoplastic polyurethane (TPU) fiber with low shrinkage, in particular at a high spinning speed, and the use of the fiber.

BACKGROUND

Most of the TPU fibers on the market possess high elasticity and low modulus. High-elasticity TPU fibers have been used in the form of auxiliary materials in fabrics, commonly referred to as spandex, and cannot be used as the main raw material in fabrics due to their performance problems. It acts as an elastic component in fabrics. In contrast, low-elasticity and high-modulus TPU fiber can be used as the main raw material in fabrics. The low-elasticity and high-modulus TPU fibers possess similar rigidity to that of the polyamide and polyester fibers, together with high tenacity, high modulus and low elongation, which make them useful in the same application fields as polyamide and polyester fibers.

The low-elasticity and high-modulus TPU fibers could be used as both of the auxiliary material and the main material in fabrics. When used as the auxiliary material, it provides more fabric design idea/potentiality to the designers. On the other hand, when used as the main material, it can produce whole TPU (100% TPU) products such as shoe upper to replace the current PA and PET uppers. The 100% TPU upper can be 100% recycled, and the abrasion resistance will be better than uppers made by PA or PET fiber. This could broaden the application fields of the TPU fibers. Therefore, the low-elasticity and high-modulus TPU fibers have received increasing attention nowadays.

The process for preparing the high-modulus TPU fibers requires a high taking-up speed (winding speed) (see WO 2018/146192). However, TPU fibers produced by such a high-speed (>2000 m/min) melt-spinning process will shrink a lot (usually 20%-35%) when being treated by boiling-water or steam. Articles knitted by these fibers will also shrink a lot (usually 20%-40%) during steaming or ironing process. This large shrinkage will destroy the original good haptics of the articles and make them feel like plastics. Moreover, the large shrinkage will also decrease the original article size seriously, thus make the article dense and hard. Therefore, it needs to reduce the shrinkage of the TPU fiber.

A number of processes have been disclosed in the prior art to obtain the low-shrinkage fibers.

US 2009/0311529 A1 discloses the production of a high-tenacity and high-modulus TPU monofilament (rigid TPU monofilament) with reduced shrinkage as low as 10% at 140° C. by Extruding process, then Orientation process and finally Dynamic Annealing process. The monofilament produced by the process has a very high denier from 80 to 20,000. In the process, the extrudates have a diameter of 0.95 mm. After quenched in water, they go to the Orientation process. That means, these two steps are not continuous. Furthermore, the high-speeding spinning technique was not touched at all by this invention.

KR 100587903 discloses a low-shrinkage PU fiber obtained by a dry-spinning process. The elastic fiber subjected to a spinning process is heat-treated at above 100° C. for 0.01 to 0.05 sec in a heat treatment apparatus (14), such as a heating tube having a length of 20 to 30 cm or a heating roll. The obtained PU elastic fiber has a boiling water shrinkage rate of less than 7% and a heat shrinkage rate of less than 5% after treatment in a heated air oven at 100° C. for 1 hr. It uses a dry-spinning process in this application. It does not mention the melt-spinning process, especially at a high speed.

U.S. Pat. No. 5,066,439 discloses a continuous spin-draw process for making dimensionally stable polyester fiber having high strength and low shrinkage by melt spinning polyethylene terephthalate, drawing, applying a commingling treatment, and then applying a relaxation heat treatment. During the drawing step, a heated plate with a temperature of 250 to 500° C. is used in order to assist in the relaxation of the fiber.

US 2009/0124149 A1 discloses multi-filament polyamide yarns having high tenacity and low shrinkage, and a process for making such yarns. The process involves spin-drawing the molten nylon, relaxing and controlling the yarn tension, and then winding the yarn.

CN 102168319 B discloses a high-strength, high-modulus and low-shrink polyester industrial yarns, and a process for preparing the yarns. The process involves relaxing the yarns after spinning.

It has not been disclosed in the prior art a process for preparing a TPU fiber with low shrinkage and high tenacity, especially with shrinkage of less than 10%, at a high spinning speed.

SUMMARY OF THE INVENTION

Thus, an object of the present invention is to provide a process for producing a TPU fiber with low shrinkage, comprising (a) melt-spinning a composition comprising a TPU resin, at a spinning rate of 2000-5000 m/min; and (b) heat setting the resulted fiber.

Another object of the present invention is to provide a fiber obtainable by the process.

Another object of the present invention is to provide a fabric comprising the fiber.

A further object of the present invention is to provide a product comprising the fabric, wherein the product is shoes, pants, T-shirt, chair mesh, watch band, or hair band.

DETAILED DESCRIPTION OF THE INVENTION

In the first aspect, the present invention relates to a process for producing TPU fiber, comprising (a) melt-spinning a raw material composition comprising a TPU resin, at a spinning rate of 2000-5000 m/min; and (b) heat setting the resulted fiber.

The individual steps will be explained in detail in the follows.

Step (a): Melt Spinning

Melt spinning is a technique in which a raw material composition in a molten state obtained by heating the raw material composition to a temperature equal to or higher than the melting point by using an extruder or the like is discharged from a spinning nozzle into a gas phase (for example, into the air or into the air cooled if necessary). The positioning of the nozzle is not limited. However, it is preferable to direct the nozzle downward so that the molten composition (fiber) is discharged downward (drawn down). The discharged molten fiber is cooled and solidified in the gas phase while being made fine, and then is taken up at a certain speed.

It is also possible to melt a main component (TPU) of the raw material composition separately from other component(s) of the raw material composition so that the molten main component is mixed with others just before discharging from the nozzle.

The apparatus for melt spinning is not particularly limited, and an example thereof is shown in FIG. 1. The apparatus for producing fiber includes an extruder (not shown), a spin pack 1 and a winder 2. The spin pack is known in the art, and primarily consists of melt reservoir and spinneret.

A raw material composition or the main component thereof, for example, formed as pellets are fed from a feeder opening to the extruder, melted in the extruder, and then discharged to be a molten fiber from the nozzle (spinning nozzle) of a spin pack into a gas phase.

When using one or more additive (the other component) such as a crosslinker, at least one mixer such as a static or a dynamic mixer, preferably a static mixer may be provided in the apparatus. In this case, the main component comprising the TPU, in one preferred embodiment consisting of the TPU, is molten in the extruder separately from the crosslinker; the crosslinker is mixed with the molten main component by using the mixer; and then the mixed composition in a molten state (i.e., the raw material composition in the molten state) is discharged from the nozzle of the spinning head. The TPU of the raw material composition is crosslinked with the crosslinker during the melt spinning process. Or else, the dried TPU granules are melted in extruder and the crosslinker (0-20%) is fed at end of the extruder. The blend of crosslinker and TPU melt passes through the mixer and the melt pipe line, and after metering, it is pressed into the spin pack, and finally goes out of the spinneret.

After going out of the spinneret, the extruded TPU fiber is drawn or oriented by passing through a series of godet rollers (such as GR1, GR2 and GR3 in FIG. 1) that are set up at different linear speed ratios. It should be noted that the number of the godet rollers is not limited to 3, actually, it could be 2 or more but no more than 6, such as 2, 3, 4, 5, or 6. However, it is preferred that there are 3 godet rollers.

During the spinning, the fiber is subjected to a shrinkage controlling treatment. This treatment is carried out by heating up the godet rollers to certain surface temperature in order to fix the orientation in the TPU fiber, so that the shrinkage caused by the high-speed spinning could be controlled, for examples to less than 30%.

The surface temperatures and speeds of GR1, GR2 and GR3 may be as follows,

-   -   GR1: the temperature is 30-150¹, preferably 60-100¹, and         independently, the speed is 1000-6000 m/min, preferably         1000-4500 m/min,     -   GR2: the temperature is 60-200¹, preferably 100-160¹, and         independently, the speed is 2000-6000 m/min, preferably         2000-4500 m/min,     -   GR3: the temperature is 30-150¹, preferably 60-100, and         independently, the speed is 2000-6000 m/min, preferably         2000-4500 m/min.

In the present invention, the speed refers to the peripheral speed of the godet, unless otherwise indicated.

As the last step of the melt-spinning process, the TPU fiber is wound onto a bobbin through the winder 2 (shown in FIG. 1) under a high winding speed of 2000-6500 m/min, preferably 2000-5000 m/min.

In the present invention, the spinning rate means the take-up (winding) speed.

Moreover, after going out of the spinneret and before reaching the godet rollers, the fiber may be oiled. The oiling step could lubricate the fiber and reduce the friction between the fiber and the metallic/ceramic parts of the spinning line; allow dissipation of the static charges generated due to contact of fiber with the machine parts; and keep the fibers together, so that unwinding from the spun cake becomes easier. The fiber may be oiled by any conventional spinning oil.

The gas phase for the melt-spinning is not particularly limited, and may be various gas phases such as an inert gas atmosphere and the air atmosphere, and preferably the air atmosphere (air) from the viewpoint of the cost. The temperature of the gas phase can be any temperature lower than the melting point of the raw material composition, and is from −10° C. to 50° C. and more preferably from 10° C. to 40° C. in consideration of the cost.

The spinning conditions other than the spinning rate are not particularly limited, but are preferably set as follows.

Spinning Temperature

The spinning temperature is defined as, for example, the heating temperature not only in the extruder, but also that in the polymer pipe and in the spin pack. The spinning temperature is not particularly limited, and can be appropriately varied according to the melting point of the raw material composition; from the viewpoint of spinnability, the spinning temperature is usually 180° C. or higher, preferably 200° C. or higher, more preferably 220° C. or higher, but preferably no higher than 240° C. Especially when using a TPU having high hardness (for example, shore 60D or more), a higher spinning temperature (for example, more than 220° C., preferably 225° C. or more) enables the spinning at a higher spinning rate. From the viewpoint of the suppression of the thermal decomposition of the raw material composition, the spinning temperature is usually 240° C. or lower, and preferably 235° C. or lower.

Raw Material Composition

The raw material may comprise a resin comprising, more preferred essentially consisting of a TPU. The term “essentially consisting” means that the resin comprises the TPU and optionally unintended materials such as residues, contaminants or the like. In other words, the resin comprises 95% by weight (wt. %) or more of TPU(s), preferably 99 wt. % or more, or preferably 99.5 wt. % or more, especially 99.9 wt. % or more, even 100 wt. % of TPU(s). Such TPU is not limited and one or more of TPUs can be used. Hereinafter, the useful TPUs will be explained.

TPU

As to the TPU used in the present invention, there is not any particular requirement imposed. The TPU is generally obtained, without being particularly limited, by allowing an (a) isocyanate, preferably an organic diisocyanate, a (b) polyol, and a (c) chain extender (a polyol shorter in the chain length than the long chain polyol, usually a short chain diol) as the essential components to react with each other, if necessary, in the presence of a (d) catalyst and/or an (e) aid (auxiliary agent). In a preferred embodiment the chain extender has a molecular weight from 50 g/mol to 499 g/mol. The polyol, also referred to as long chain polyol has a number average molecular weight from 500 g/mol to 8×103 g/mol. The reaction can be a one-stage reaction allowing the whole of the essential components (a) to (c) to react with each other in one stage in a preferred embodiment in the presence of the optional components (d) and (e), or a reaction having a plurality of stages allowing two or more components of (a) an (b) to react with each other to form a prepolymer and then allowing the prepolymer and the rest of the essential components to react with each other, preferably in the presence of the components (d) and (e).

The hardness of the TPU is measured in accordance with DIN ISO 7619-1, which is generally Shore 80 A to Shore 80 D, preferably Shore 80 A to Shore 74 D, and more preferably Shore 90 A to Shore 70 D.

The weight-averaged molecular weight (Mw) of the TPU is not limited, and generally from 50 000 to 800 000, preferably from 80 000 to 600 000, more preferably from 80 000 to 400 000.

As (a) isocyanate, it is possible to use generally known aromatic, aliphatic, and/or araliphatic isocyanates, and preferably diisocyanates are used. Specifically, it is possible to use one or more selected from, for example, the following: 2,2′-, 2,4′ and/or 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 2,4- and/or 2,6-tolylene diisocyanate (TDI), diphenylmethane diisocyanate, 3,3′-dimethyldiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and/or phenylene diisocyanate, tri, tetra, penta, hexa, hepta and/or octamethylene diisocyanate, 2-methylpentamethylene-1,5-diisocyanate, 2-ethylbutylene-1,4-diisocyanate, 1,5-pentamethylene diisocyanate, 1,4-butylene diisocyanate, 1-diisocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (isophorone diisocyanate, IPDI), 1,4- and/or 1,3-bis(isocyanatomethyl)cyclohexane (HXDI), 1,4-cyclohexane diisocyanate, 1-methyl-2,4- and/or -2,6-cyclohexane diisocyanate and/or 4,4′-, 2,4′- and 2,2′-dicyclohexylmethane diisocyanate. More preferable isocyanates are 2,2′-, 2,4′- and/or 4,4′-diphenylmethane diisocyanate (MDI), 1,5-naphthylene diisocyanate (NDI), 2,4- and/or 2,6-tolylene diisocyanate (TDI), hexamethylene diisocyanate (HDI) and/or IPDI, in particular, MDI and/or HDI, and the most preferable isocyanate is MDI.

As (b) polyol, compounds generally known as isocyanate reactive compounds can be used. For example, polyester polyol, polyether polyol, polycaprolactone polyol and/or polycarbonate polyol can be used; these are customarily covered by the term “polyol”. Preferably, the component (b) may be polyether polyol or polyester polyol. In certain cases, it is possible to use the mixture of polyether polyol with polyester polyol. The generally used polyols have number average molecular weights of, for example, 500 g/mol to 8,000 g/mol, preferably 600 g/mol to 6,000 g/mol, more preferably 700 g/mol to 4,000 g/mol, even more preferably 800 g/mol to 3,000 g/mol. Molecular masses of the polyols herein are number average molecular weights.

Among such polyols, polyether polyol or polyester polyol may be preferably used, and among these two polyols, polyether polyol may be preferably used considering microorganism corrosion resistance and water resistance, and polyester polyol may be preferably used considering mechanical property.

The polyether polyols may be obtained by known methods, for example by polymerization of alkylene oxides with addition of at least one starter molecule which comprises from 2 to 8, preferably from 2 to 6, reactive hydrogen atoms in the presence of a catalyst. As the catalyst, it is possible to use alkali metal hydroxides such as sodium or potassium hydroxide or alkali metal alkoxides such as sodium methoxide, sodium or potassium ethoxide or potassium isopropoxide or, in the case of cationic polymerization, Lewis acids such as antimony pentachloride, boron trifluoride etherate or bleaching earth as the catalyst. Furthermore, double metal cyanide compounds, known as DMC catalysts, can also be used as the catalyst.

As the alkylene oxide, preference is given to using one or more compounds having from 2 to 4 carbon atoms in the alkylene radical, e.g. ethylene oxide, 1,3-propylene oxide, tetrahydrofuran, 1,2- or 2,3-butylene oxide, in each case either alone or in the form of mixtures, and preferably ethylene oxide, 1,2-propylene oxide and/or tetrahydrofuran, most preferably tetrahydrofuran.

Possible starter molecules are, for example, ethylene glycol, diethylene glycol, glycerol, trimethylolpropane, pentaerythritol, sugar derivatives such as sucrose, sugar alcohol such as sorbitol, methylamine, ethylamine, isopropylamine, butylamine, benzylamine, aniline, toluidine, toluenediamine, naphthylamine, ethylenediamine, diethylenetriamine, 4,4′-methylenedianiline, 1,3-propanediamine, 1,6-hexanediamine, ethanolamine, diethanolamine, triethanolamine and other dihydric or polyhydric alcohols or monofunctional or polyfunctional amines.

Examples of polyether polyols can also include a ring-opening polymer of tetrahydrofuran (polytetramethylene glycol, PTMEG), natural oil-based polyols like castor oil or alkoxylation modified natural oils or fatty acids.

The polyester polyol may be prepared by condensation of polyfunctional alcohols having from 2 to 12 carbon atoms with polyfunctional carboxylic acids having from 2 to 12 carbon atoms. The polyfunctional alcohols or polyfunctional carboxylic acids may have a functionality of around 2. The examples of the polyfunctional alcohols may be ethylene glycol, diethylene glycol, butanediol, or a combination thereof. The examples of the polyfunctional carboxylic acids may be succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, decanedicarboxylic acid, maleic acid, fumaric acid, phthalic acid, isophthalic acid, terephthalic acid, the isomers of naphthalenedicarboxylic acids, or the ester or anhydrides of the acids mentioned.

The polyether polyol or the polyester polyol used herein has a hydroxyl number of from about 15 to about 225 mg KOH/g, preferably from about 20 to about 190 mg KOH/g, more preferably from about 30 to about 160 mg KOH/g, most preferably from about 40 to about 140 mg KOH/g.

As (c) chain extenders, it is possible to use bifunctional or trifunctional amines and alcohols, in particular diols, triols or both. Bifunctional compounds of this type are referred to as chain extenders and trifunctional or higher-functional compounds are referred to as crosslinkers. As examples, it may be mentioned ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,2-pentanediol, 1,3-pentanediol, 1,10-decanediol, 1,2-dihydroxycyclohexane, 1,3-dihydroxycyclohexane, 1,4-dihydroxycyclohexane, diethylene glycol and triethylene glycol, dipropylene glycol and tripropylene glycol, 1,6-hexanediol and bis(2-hydroxyethyl) hydroquinone; triols such as 1,2,4-trihydroxycyclohexane, 1,3,5-trihydroxycyclohexane, glycerol and trimethylolpropane. A particularly preferable (c) chain extender includes 1,3-propanediol, 1,4-butanediol or 1,6-hexanediol. In certain cases, it is possible to use the mixture of two chain extenders.

In order to regulate the hardness of the TPU, the molar ratios between the constitutional unit components (b) and (c) can be varied over relatively wide ranges of molar ratios. The molar ratio of the component (b) to the total amount of the chain extender (c) is 10:1 to 1:10, in particular the range from 1:1 to 1:5 is useful, and with the increase of the content of (c), the hardness of the TPU increases.

Examples of (d) catalyst, an optional component, without being particularly limited to: trimethylamine, dimethylcyclohexylamine, N-methylmorpholine, N,N′-dimethylpiperazine, 2-(dimethylaminoethoxy)ethanol, diazabicyclo(2,2,2)octane and the analog thereof; further, in particular, organometallic compounds such as titanium ester; iron compounds such as iron (III) acetylacetonate; tin compounds such as tin diacetate, tin dioctoate and tin dilaurate; and tin dialkyl salts of aliphatic carboxylic acids such as dibutyltin diacetate and dibutyltin dilaurate and the equivalents thereof. The catalyst is usually used in an amount of 0.0001 to 0.1 part by mass in relation to 100 parts by mass (b) long chain polyol.

Examples of the aid (e), an optional component, include: a surfactant, a nucleating agent, a gliding and demolding aid, a dye, a pigment, an antioxidant (for example, in relation to hydrolysis, light, heat and discoloration), an ultraviolet absorber, a flame retardant, a reinforcing agent, a plasticizer or a flowability improver and a cross-linking agent; one or more selected from these can be used.

The TPU used may be the polyether or polyester-based TPU. Here, the term “polyether-based TPU” means a TPU prepared by using one or more polyether polyols as a main component (for example, 50 wt. % or more) of (b) long chain polyol. This also applies to the polyester-based TPU.

As the TPU produced from the components (a) to (c), and optionally from (d) and (e), commercially available products can also be used, such as Elastollan® TPU from BASF.

The raw material composition may comprise the above TPU as the main component. However, further additives can also be used in the raw material composition. The additive is not particularly limited; however, it is possible to add and use one or more of the additives used in the fiber field such as a flame retardant, a filler, a pigment, a dye, an antioxidant, an ultraviolet absorber and a light stabilizer.

Among of additives, a crosslinker may be used together with the TPU. Any type of crosslinker can be used, however, it is preferable to use one or more of crosslinkers selected from reacted compounds which are prepared from one or more (i) polyols; one or more (ii) isocyanates, and optionally other compound(s). Considering properties of the final product (fiber), one or more of polyether or polyester crosslinker may be preferably used. Usually, the molecular weight of the crosslinker is lower than that of the TPU above.

The crosslinker used is an NCO-terminated prepolymer with a functionality of 1.5 to 3, preferably 1.6 to 2.5, and more preferably 1.8 to 2.1. The prepolymer has an NCO content of 3 to 15 wt. %, preferably 4 to 10 wt. %, and more preferably 4 to 8 wt. %.

The polyether crosslinker is prepared by using (i) polyol where at least 50 wt. %, preferably at least 80 wt. %, more preferably at least 95 wt. % of (i) polyol is selected from one or more polyether polyols. In other words, the polyether crosslinker contains one or more units derived from the polyether polyol (polyether polyol unit).

It is not particularly limited but the (i) polyether polyol may be selected from a ring-opening polymer of tetrahydrofuran (polytetramethylene glycol, PTMEG), alkylene oxides (in particular, ethylene oxide, propylene oxide and mixtures of these) and alcohol adducts. More preferably, (i) polyether polyol has a number average molecular weight (Mn) of 500 g/mol to 4.0×10³ g/mol, more preferably 600 g/mol to 3.0×10³ g/mol, particularly 0.8×10³ g/mol to 2.0×10³ g/mol.

The polyester crosslinker is prepared by using (i) polyol where at least 50 wt. %, preferably at least 80 wt. %, more preferably at least 95 wt. % of (i) polyol is selected from one or more polyester polyols. In other words, the polyester crosslinker contains one or more units derived from the polyester polyol (polyester polyol unit).

Preferably, (i) polyester polyol has a number average molecular weight (Mn) of 600 g/mol to 4.0×103 g/mol, more preferably 800 g/mol to 3.0×103 g/mol, particularly 1.0×103 g/mol to 3.0×103 g/mol.

(ii) Isocyanate is not particularly limited but may be selected from an aromatic, aliphatic or cycloaliphatic diisocyanate. For example, (ii) isocyanate may be selected from compounds explained above for (a) isocyanate of the preferable TPUs. Among of isocyanates, MDI may be preferably used for the crosslinker.

The amount of the polyether or polyester crosslinker is not limited but it is preferable to set the amount to 1 wt. % or more, 3 wt. % or more, even 5 wt. % or more based on the total amount of the raw material composition. When melting the main component (TPU resin) separately from the other(s) (one or more crosslinkers and/or one or more other additives), the total amount of the raw material composition may be obtained by summing amounts of the main component and others.

The upper limit of the amount of the crosslinker is not particularly limited but in preferred embodiments the upper limit is 25 wt. % or less, 20 wt. % or less, more preferably 15 wt. % or less, based on the total amount of the raw material composition.

It is also possible to use a non-polyether or non-polyester crosslinker where at least 50 wt. % of (i) polyol is selected from the non-polyether polyol (polyol other than polyether polyol) or the non-polyester polyol (polyol other than polyester polyol), such as polycaprolactone- and/or polycarbonate-polyol.

In a preferred embodiment of the present invention, the TPU is prepared from (a) PTMEG, (b) MDI, and (c) 1,4-butanediol.

Step (b): Heat Setting

After melt spinning of the TPU, the fiber is subjected to heat setting.

Heart setting could be carried out in two modes: an off-line mode (Mode A) and an on-line mode (Mode B).

In Mode A, the bobbin comprising the melt-spun TPU fiber is kept in a heating oven to make the shrinkage happen. During the heat setting, the bobbin comprising the melt-spun TPU fiber is placed on a scaffold, and optionally a heating media is passed through the oven. The oven may be vacuum or atmosphere such as air, nitrogen (N₂) or water vapor. The heating media may be vapor, dry air or dry nitrogen. The heat setting temperature of the off-line mode may be 70-130′, preferably 80-120° C., more preferably 90-110° C.; and the heat setting time of the off-line mode may be 30-240 minutes, preferably 60-200 minutes, more preferably 60-180 minutes.

The TPU fiber produced by Mode A will show very low shrinkage of less than 6%, and preferred is 0-3%.

In Mode B, The TPU fiber produced by the melt-spinning process is passed through a set of hot godet rollers without further drawing or orienting, wherein the number of the godet rollers are, for example, 2 or more, but preferably no more than 6, then the fiber is rewound onto another bobbin. An example of the apparatus for Mode B is shown in FIG. 2. The set of hot godet rollers 3 (including three godet rollers as refer to GR4, GR5 and GR6) are heated up to certain surface temperatures to make shrinkage happen to the TPU fiber. Since shrinkage will happen step by step when the TPU fiber passing through each roller, the rotating speeds of the rollers and the winder are set as: GR4≥GR5≥GR6≥Winder, the surface temperature of the rollers and winder was set as: GR5≥GR6≥GR4≥Winder.

The surface temperatures and speeds of GR4, GR5 and GR6 may be as follows, wherein the above relationships of the surface temperatures and speeds of the godet rollers must be followed,

-   -   GR4: the temperature is 70-150° C., preferably 100-130° C., and         independently, the speed is 300-900 m/min, preferably 400-800         m/min,     -   GR5: the temperature is 100-180° C., preferably 130-160° C., and         independently, the speed is 300-800 m/min, preferably 400-700         m/min,     -   GR6: the temperature is 80-140° C., preferably 130-160° C., and         independently, the speed is 200-800 m/min, preferably 350-650         m/min.

The speed and temperature of the winder are not limited, as long as they meet the above relationships. For example, the winder may have a room temperature and a speed of 300-600 m/min.

The TPU fiber produced by Mode B will show very low shrinkage less than 10%, and preferred is less than 5%.

After the heat setting, the TPU fiber is rewound once again. During this period, oil may be coated onto the fiber for easy processing in the following twisting process.

After oiling, the TPU fiber will usually be twisted by S or Z direction to decrease the friction in the knitting process afterwards. It is also possible to omit the twisting process according to different knitting technology and performance requirement.

The TPU fiber with DPF (denier per fiber) in the range of 3-50 produced by the present process has low shrinkage of less than 10%, preferably less than 6%, a high tenacity of more than 1.5 cN/dtex, preferably more than 2.0 cN/dtex, and an elongation at break of less than 150%, preferably less than 100%, more preferably less than 80%. Moreover, the TPU fiber of the present invention has a 3-50 DPF, preferably 5-30 DPF, more preferably 6-20 DPF.

Therefore, in the second aspect, the present invention relates to a fiber obtainable by the process. The fiber of the present invention possesses the above advantageous properties.

Such properties make the fiber well suitable for manufacturing fabric. The fabric may be used in shoe, pants, T-shirt, chair mesh, watch band, etc. The fabric prepared by the present process show shrinkage of less than 10%, preferably less than 5%

The present invention combines the high-speed spinning process with the heat-setting process. This allows to produce a TPU fiber in high productivity, which could greatly decrease the cost. Moreover, the obtained TPU fiber has very low shrinkage of <10%, which makes it well suitable as the main raw material in fabrics. Therefore, the size, property and haptics of the fabrics produced by the fiber could be well controlled during steaming or ironing process.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows an example of the apparatus for melt spinning, wherein the reference number 1 represents a spin pack, and 2 represents a winder, and GR1, GR2 and GR3 are godet rollers.

FIG. 2 shows an example for the apparatus for Mode B, wherein the reference number 3 represents a set of heated rollers GR4, GR5 and GR6, and 4 represents a winder.

EXAMPLES

Measuring and Test Methods

The measuring and test methods are shown in Table 1.

TABLE 1 Property Unit Testing standard Denier per filament (DPF) De GB/T 14343-2008 Tenacity cN/dtex GBT 14344-2008 Elongation at break % GB/T 14343-2008 Shrinkage in boiling water of the fiber % GB/T 6505-2008, skein method

Moreover, the shrinkage of the fabric is measured as follows: taking out of a piece of fabric with a size of 50 cm×50 cm as a sample; drawing two marks on the sample with a crayon; measuring the distance between the two marks and denoted as L₀; ironing the sample for 15 seconds by using a commercial steam iron under the conditions for ironing synthetic fibers; then cooling to the room temperature, measuring the distance between the two marks and denoted as L₁; calculating the shrinkage of the fabric according to the formula of shrinkage=(L₀−L₁)/L₀×100%.

Materials

The materials used in the examples are as follows.

One polyether based Elastollan® product SP9519 with a weight-average molecular weight of 80 000-200 000 based on PTMEG, MDI and 1,4-butanediol (obtained from BASF, having a Shore D hardness of 60-64) was used for preparing the fiber.

Finish oil: a finish oil (obtained from Takemoto Oil & Fat Co., Ltd) was used during the spinning process.

The general description of the process used in the examples

By using the apparatus shown in FIG. 1, the TPU is spun out of the spin pack at a temperature of 230° C., and the spun fibers are passed through the godet rollers GR1, GR2 and GR3 with the temperatures and speeds as indicated in Table 2. Then, the resulted fibers are subjected to heat setting in Mode A and B, respectively, and the conditions and the results are shown in Table 3 and 4, respectively. The fiber is oiled after spinning out from the spin pack and before reaching godet roller GR1; moreover, after the heat setting, the fiber is oiled again for easy processing in the following twisting process.

TABLE 2 Experiment No. Example 1 1-1 1-2 1-3 Condition of TPU Fiber Making Shrinkage GR1 ° C. 60 80 80 control during temperature spinning GR2 ° C. 100 140 140 temperature GR3 ° C. 60 80 80 temperature GR1 speed m/min 2500 2800 3300 GR2 speed m/min 2600 3000 3500 GR3 speed m/min 2800 3300 3800 Winder speed m/min 3000 3500 4000 Property of the Fiber DPF De 15 10 6 Tenacity cN/dtex 2.4 2.7 3.1 Elongation at break % 60 50 45 Shrinkage % 25 28 33 Property of the Fabric Shrinkage % 27 30 35

TABLE 3 Experiment No. Example 2 2-1 2-2 The fiber Sample No. 1-1 produced in Example 1 was treated by Mode A. Condition of TPU Fiber Heat Setting Mode A Oven ° C. 80 110 temperature Oven heating min 120 60 time Property of the Fiber DPF De 17 17.5 Tenacity cN/dtex 2.3 2.3 Elongation at break % 66 68 Shrinkage % 3 2.6 Property of the Fabric Shrinkage % 4.5 4

TABLE 4 Experiment No. Example 3 3-1 3-2 The fiber Sample No. 1-1 produced in Example 1 was treated by Mode B. Condition of TPU Fiber Heat Setting Mode B GR4 speed m/min 500 650 GR5 speed m/min 470 630 GR6 speed m/min 450 600 Winder speed m/min 400 550 GR4 temperature ° C. 120 120 GR5 temperature ° C. 140 140 GR6 temperature ° C. 120 120 Property of the Fiber DPF De 16.6 16.4 Tenacity cN/dtex 2.3 2.3 Elongation at break % 65 64 Shrinkage % 4.7 5.2 Property of the Fabric Shrinkage % 6 7

In Example 1, the fibers are only subjected to the shrinkage controlling treatment during spinning without heat setting treatment after the spinning; while in Example 2, the fibers are subjected to bath of the shrinkage controlling treatment during spinning and the heat setting treatment in Mode A, and in Example 3, the fibers are subjected to subjected to bath of the shrinkage controlling treatment during spinning and the heat setting treatment in Mode B.

As is evident from the above, the shrinkages of the fibers resulted from Example 2 and 3 are much less than those of Example 1, at the same time, the elongation at break of the fibers resulted from Example 2 and 3 are higher than those of Example 1. 

1: A process for producing a TPU fiber, comprising: (a) melt-spinning a composition comprising a TPU resin into a fiber; and (b) heat setting the fiber. 2: The process according to claim 1, wherein the melt-spinning is carried out at a spinning rate of 2000-6500 m/min. 3: The process according to claim 1, wherein (a) comprises passing a spun fiber through 2 or more, but no more than 6 godet rollers. 4: The process according to claim 3, wherein the godet rollers are heated. 5: The process according to claim 3, wherein there are 3 godet rollers, GR1, GR2, and GR3. 6: The process according to claim 5, wherein a temperature of GR1 is 30-150° C., a temperature of GR2 is 60-200° C., and a temperature of GR3 is 30-150° C. 7: The process according to claim 5, wherein a speed of GR1 is 1000-6000 m/min, a speed of GR2 is 2000-6000 m/min, and a speed of GR3 is 2000-6000 m/min. 8: The process according to claim 1, wherein the heat setting is carried out by keeping a spun TPU fiber in a heating oven. 9: The process according to claim 8, wherein a heat setting temperature is 70-130° C. and a heat setting time is 30-240 minutes. 10: The process according to claim 1, wherein the heat setting is carried out by making a spun fiber pass through a set of hot godet rollers without further drawing or orienting. 11: The process according to claim 10, wherein a number of the hot godet rollers is 2 or more, but not more than
 6. 12: The process according to claim 10, wherein there are 3 hot godet rollers, GR4, GR5, and GR6. 13: The process according to claim 12, wherein a temperature of GR4 is 70-150° C., a temperature of GR5 is 100-180° C., and a temperature of GR6 is 80-140° C. 14: The process according to claim 12, wherein a speed of GR4 is 300-900 m/min, a speed of GR5 is 300-800 m/min, and a speed of GR6 is s 200-800 m/min. 15: The process according to claim 1, wherein a hardness of the TPU is from Shore 80 A to Shore 80 D, as measured according to DIN ISO 7619-1. 16: The process according to claim 1, wherein the TPU is a reaction product of; (a) isocyanate, (b) polyol, and (c) chain extender; and optionally, in the presence of (d) catalyst and/or (e) auxiliary agent. 17: The process according to claim 16, wherein the isocyanate is at least one selected from the group consisting of 2,2′-, 2,4′, and 4,4′-diphenylmethane diisocyanate (MDI); 1,5-naphthylene diisocyanate (NDI); 2,4- and 2,6-tolylene diisocyanate (TDI); diphenylmethane diisocyanate; 3,3′-dimethyldiphenyl diisocyanate, 1,2-diphenylethane diisocyanate and phenylene diisocyanate; tri, tetra, penta, hexa, hepta, and octamethylene diisocyanate; 2-methylpentamethylene-1,5-diisocyanate; 2-ethylbutylene-1,4-diisocyanate; 1,5-pentamethylene diisocyanate; 1,4-butylene diisocyanate; 1-diisocyanato-3,3,5-trimethyl-5-isocyanatomethyl cyclohexane (IPDI); 1,4- and 1,3-bis(isocyanatomethyl)cyclohexane (HXDI); 1,4-cyclohexane diisocyanate; 1-methyl-2,4- and -2,6-cyclohexane diisocyanate; and 4,4′-, 2,4′-, and 2,2′-dicyclohexylmethane diisocyanate. 18: The process according to claim 16, wherein the polyol is selected from the group consisting of polyester polyol, polyether polyol, polycaprolactone polyol, and polycarbonate polyol. 19: The process according to claim 16, wherein the chain extender is selected from the group consisting of ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,2-pentanediol, 1,3-pentanediol, 1,10-decanediol, 1,2-dihydroxycyclohexane, 1,3-dihydroxycyclohexane, 1,4-dihydroxycyclohexane, diethylene glycol, triethylene glycol, dipropylene glycol, tripropylene glycol, 1,4-butanediol, 1,6-hexanediol, bis(2-hydroxyethyl) hydroquinone; triols, and a combination thereof. 20: A TPU fiber obtained by the process according to claim
 1. 21: A fabric comprising the TPU fiber according to claim
 20. 22: A product comprising the fabric according to claim 21, wherein the product is a shoe, pants, T-shirt, chair mesh, watch band, or hair band. 